The spontaneous conversion of pre-stages of coating material into the coating material itself under certain conditions is employed according to the prior art in order to guarantee the self-healing properties of coatings or coating materials. Such a self-healing layer or the coating material (enamel) used for this purpose is for example to be taken from EP 355 028 A1. This here involves a coating of roof tiles, which is intended to extend their useful life under weather conditions. To this end a lower enamel layer of the roof tile contains an aromatic ketone, which in the case of UV-irradiation or under the influence of sunlight activates the cross-linking of lower enamel layers and thus effects a healing of mechanical defects through the spontaneous creation of chemical compounds. Use of the word ‘spontaneously’ in connection with this invention should be taken to mean that the self-healing process is not set in motion as a result of the external influence of a control process—for example after monitoring by a human agency—but is instead set in motion in the environment of the location of use of the surface layer—for example atmospheric weather conditions—automatically based on the properties of the surface layer and the environmental conditions. The control of the self-healing process is preferably undertaken by means of UV-irradiation (solar radiation), where the dosation of the UV-irradiation cannot be influenced, but rather depends on the weather conditions in the area of application. The solar radiation in Mediterranean countries is, for example, higher on average and precipitation lower than for example in the Nordic countries. The setting of the parameters for self-healing of the enamel thus gives rise to certain problems.
Other self-healing enamel systems according to the prior art dispense with active components in the coating, but instead solely make use of a physical residual flow capability of a coating after hardening, for example in order to heal scratches that may have occurred. Such enamels are based inter alia in the outermost layer on a polyurethane compound. If such a so-called PUR-enamel is heated, for example by means of solar radiation, the enamel layers flow, whereby damage of the same is leveled out. The comparatively high flow capability of the coating required for this does however presuppose a low cross-linking density. In the case of many applications this leads to inadequate mechanical resistance, which for example does not fulfill the requirements for automotive applications in respect of scratch-proof properties or resistance to chemicals.